The study region can be partitioned in one, two, or three directions along the coordinate axis, yielding multiple adjacent boxes called grid cells.
To reduce the impact of multiple presence within some grid cells due to more extensive sampling, we set MaxEnt to "remove duplicate presence records".
We gridded baseline mortality rates, baseline YLL, and the fraction of the population ≥ 30 years of age to the MOZART-2 grid, and for grid cells overlapping multiple countries, we calculated area-weighted averages using a geographic information system program.
Thus, from the 81 records, we had 45 training points and 19 test points, after excluding multiple occurrences per grid cell.
However, unlike place cells, grid cells each have multiple firing fields that tile the entire environment in a regular triangular pattern.
During exploration of an environment individual grid cells are active at multiple locations that together follow a hexagonal grid-like organization.
The coordinate map that grid cells make up is composed of multiple layers, each with a different periodic distance between grid points.
However, a naive model where place cells are sums of grid cells would also suggest that the multiple place fields would be arranged in an orderly, possibly periodic, manner.
However, Derdikman et al. (2009) showed that in fact, place cells and grid cells recorded in an environment comprising multiple identical tracks actually repeat their firing fields across tracks, with grid fields being "reset" each time the animal entered a new track and therefore not discriminating compartments.
Grid cells have periodic tuning curves they are active at multiple locations, called firing fields, and these firing fields are hexagonally arranged in the environment (Hafting et al., 2005).
